Transcriptional and metabolic modeling analyses of developing Aspergillus fumigatus biofilms reveal metabolic shifts required for biofilm maturation.

Aspergillus fumigatus is a filamentous fungus found in compost and soil that can cause invasive and/or chronic disease in humans. Diagnosis and treatment of aspergillosis often occur when A. fumigatus has formed dense networks of hyphae within the lung. These hyphal networks are multicellular, encased in an extracellular matrix, and have reduced susceptibility to contemporary antifungal drugs, similar to bacterial biofilms. A model of these dense hyphal networks observed in vivo can be recapitulated in vitro using a static, submerged biofilm culture. The mechanisms underlying filamentous fungal cell physiology at different stages of biofilm development remain to be defined. Here, we utilized RNA sequencing, in silico metabolic modeling, and molecular genetics approaches to identify A. fumigatus genes and metabolic pathways critical for biofilm development. These analyses revealed that ethanol and butanediol fermentation pathways are important for the development of a mature A. fumigatus biofilm. Correspondingly, a predicted transcription factor (silG) was observed to be required for mature biofilm development. Taken together, these data define key genes and metabolic pathways critical for A. fumigatus biofilm development. IMPORTANCE: Aspergillus fumigatus is the most common etiological agent of a collection of diseases termed aspergillosis. Chronic and invasive manifestations of aspergillosis are highlighted by the development of biofilm-like structures on and in tissue. These biofilm structures are resistant to contemporary antifungal drugs, even for strains that are susceptible by standard antimicrobial susceptibility testing methods. Consequently, understanding the mechanisms by which A. fumigatus induces, develops, and maintains biofilms to evade antifungal therapies is expected to illuminate biofilm-specific therapeutic targets. Here, we identify genes involved in fungal fermentation and regulation of transcription as important mediators of A. fumigatus biofilm development.